Air suspension systems are increasingly being utilized in vehicle suspensions, seats and cabs on semi-tracker/trailer truck rigs and other vehicles. Generally, air suspension systems include a height control valve that maintains a specified or selected height of the suspension. For instance, in semi-tracker/trailer truck rigs, the specified height is the distance between the vehicle frame and the axle. The air suspension system will sense any change in the specified height and will adjust the air pressure in the springs located between the vehicle frame and the axle. In this manner, the air suspension system maintains the specified height between the vehicle frame and the axle even with varying load weights.
The height control valve operates by selectively supplying air to, or exhausting air from, an air spring, which is located between the trailing arm and the vehicle frame. The trailing arm is provided to carrying the axle such that adjusting the air spring will correspondingly adjust the distance between the axle and the vehicle frame. Generally, the height control valve is mounted to the vehicle frame and is provided with a control arm that is connected to the trailing arm via a linkage arrangement. In this manner, as the distance between the trailing arm and the vehicle frame varies, the linkage arrangement will cause the control arm to rotate a control shaft inside the height control valve, which then controls the introduction to or exhaustion of air from the air spring. Although mechanical linkages are widely utilized to measure the varying distance between the axle and vehicle frame, other measurement transducers may be effectively utilized, such as light sensors, variable capacitors, variable resistors or any other appropriate transducer.
Generally, the height control valve comprises three air ports, an air spring port that is connected to the air spring, an inlet port that is connected to a pressurized air source and an exhaust port that is open to the atmosphere. In order to decrease the distance from the vehicle frame and the axle, the height control valve opens fluid communication between the air spring port and the exhaust port, thereby allowing pressurized air from the air spring to exhaust out to the atmosphere through the control valve. In order to increase the distance from the vehicle frame and the axle, the height control valve opens fluid communication between the inlet port and the air spring port, thereby allowing pressurized air from the pressurized air source to enter the air spring through the control valve. When the air spring is at a selected height, the valve is in a neutral position, such that the air spring port is isolated from both the inlet port and the exhaust port.
During normal operation of the vehicle, especially with heavy loads, the semi tracker/trailer will have a tendency to sway back-and-forth, from side-to-side, front -to-back or both, and oscillate due to, for instance, uneven road surfaces, weather conditions or even change in vehicle direction. These weight shifts, in turn, will cause an expansion and contraction of the distance between the axle and the vehicle frame, which will be measured by the air suspension system. The air suspension system will respond to the varying distance between the axle and vehicle frame by alternately exhausting air from and introducing air into the respective air spring to maintain the selected height between the axle and vehicle frame. It is unnecessary to maintain the selected height in this manner during vehicle operation. In fact, this constant cycling of the system is highly undesirable as it greatly reduces the lifespan of the equipment, resulting in higher maintenance costs and more vehicle down time while it is being serviced or repaired.
Varying of the air suspension system is generally utilized when, for instance, the semi tracker/trailer approaches a loading dock and the trailer height must be adjusted to match the height of the loading dock, or for connecting or disconnecting the tracker to the trailer. In addition, while the trailer is being loaded, it is advantageous for the height control valve to automatically adjust the height of and to level the trailer. However, once the height is selected and the trailer is leveled, based upon the load, it is undesirable to continually adjust the height between the axle and the vehicle frame due to minor variations in distance. However, sudden shifts in the load during vehicle operation may cause significant changes in the distance between the axle and the vehicle frame. In this case, it is important that the air suspension system adjust the air spring to maintain the selected height.
Various systems have been utilized in an attempt to minimize air consumption during normal operation of the air suspension system. The most common method has been to dampen or reduce the dynamic oscillations imparted on the valve through a mechanical damper integrated into the valve. Other methods have tried to profile the flow of air within the valve and then minimize the flow rates near the arm motions during normal operation. Both of these methods have proven moderately successful, but have not eliminated the problem.
Alternatively, electronic leveling systems have been utilized to minimize air consumption during normal operation of the air suspension system. For electronic leveling systems, a filtering algorithm is utilized in order to conserve air. This method is relatively effective, however, the cost of the electronic system is prohibitive making its usefulness in the market limited. While the electronic system may be superior to the other methods previously listed, the electronic system is also much more complicated to design, install, service and replace, further adding to the cost of the system.
U.S. Pat. No. 5,048,867 (“the '867 patent”), while directed towards solving a differing problem, namely making the actuating of the shut-off valve independent of the closure pressure loading the shut-off valve so that the valve can be furnished of small volume size, the '867 patent discloses a shut-off valve in series with a height control valve. ('867 patent, abstract and FIG. 1) However, both the height control valve and the directional control valve are controlled by control signals based on a height measuring device. ('867 patent, col. 9, lines 31–53) Therefore, the system disclosed and taught in the '867 patent will not minimize air losses to the air suspension system during normal operation of the vehicle because both the shut-off valve and the height control valve will react to oscillations of the vehicle by unnecessarily exhausting air from and adding air to the air springs based on a varying measured distance between the vehicle frame and the axel.
Therefore, what is desired is an air suspension system that will minimize cycling of equipment and air losses in the air suspension system while in normal operation of the vehicle.
It is also desired to provide a system that will selectively disconnect the control valve of the air suspension system during normal operation of the vehicle, based upon selected control criteria.
It is further desired to provide a system that will provide for various control input criteria, both manual and automatic, to selectively actuate the height control valve.
It is still further desired to provide a system that will reduce installation, maintenance and operating costs associated with air suspension systems.
It is yet further desired to provide a simple, easy to install, and highly reliable air suspension system.